package com.meirengu.utils;

import org.apache.commons.lang3.StringUtils;

import java.io.UnsupportedEncodingException;

/**
 * Created by root on 2018-01-02.
 */
public class Base64Utils {
    /**
     * Base64方法重写
     */
    public static void main(String[] args) {
        String aa = "商户私有域";
        String aaa = byteArrayToBase64(aa.getBytes());
        System.out.println(aaa);
        try {
            String bb = new String(base64ToByteArray(aaa));
            System.out.println(bb);

            String tests = encodeBuffer("【厚本金融】", "GBK");
            System.out.println(tests);
            System.out.println(decodeBuffer(tests, "GBK"));
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * 将字符数组base64字符串
     *
     * @param a 要转化的字符数组
     * @return base64字符串
     */
    public static String byteArrayToBase64(byte[] a) {
        int aLen = a.length; //总长度
        int numFullGroups = aLen / 3; //以3个byte组成以4个字符为一组的组数
        int numBytesInPartialGroup = aLen - 3 * numFullGroups; //余数
        int resultLen = 4 * ((aLen + 2) / 3); //输出长度总是4倍数，如果有余数，(aLen+2)/3保证将余数包含，并有空间放置填充符=
        StringBuffer result = new StringBuffer(resultLen);
        int inCursor = 0;
        for (int i = 0; i < numFullGroups; i++) {
            int byte0 = a[inCursor++] & 0xff;
            int byte1 = a[inCursor++] & 0xff;
            int byte2 = a[inCursor++] & 0xff;
            result.append(intToBase64[byte0 >> 2]);
            result.append(intToBase64[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
            result.append(intToBase64[(byte1 << 2) & 0x3f | (byte2 >> 6)]);
            result.append(intToBase64[byte2 & 0x3f]);
        }
        //处理余数
        if (numBytesInPartialGroup != 0) {
            int byte0 = a[inCursor++] & 0xff;
            result.append(intToBase64[byte0 >> 2]);
            //余数为1
            if (numBytesInPartialGroup == 1) {
                result.append(intToBase64[(byte0 << 4) & 0x3f]);
                result.append("==");
            } else {
                // 余数为2
                int byte1 = a[inCursor++] & 0xff;
                result.append(intToBase64[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
                result.append(intToBase64[(byte1 << 2) & 0x3f]);
                result.append('=');
            }
        }
        return result.toString();
    }

    static final char intToBase64[] = {'A', 'B', 'C', 'D', 'E', 'F', /* 索引 0 ~ 5*/
            'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',  /* 索引6 ~ 18*/
            'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',  /* 索引 19 ~ 31*/
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',  /* 索引 32 ~ 44*/
            't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',  /* 索引 45 ~ 57*/
            '6', '7', '8', '9', '.'/*原先是字符+*/, '_'/*原先是字符/ */};  /* 索引58 ~ 63*/

    /**
     * base64字符串还原为字符数组
     *
     * @param s base64字符串
     * @return 还原后的字符串数组
     * @throws Exception
     */
    public static byte[] base64ToByteArray(String s) throws Exception {
        //字符总长必须是4的倍数
        int sLen = s.length();
        int numGroups = sLen / 4;
        if (4 * numGroups != sLen)
            throw new IllegalArgumentException(
                    "字串长度必须是4的倍数");
        //余1个byte则算漏了两个byte，余2个byte则算漏掉了1个byte
        int missingBytesInLastGroup = 0;
        int numFullGroups = numGroups;
        if (sLen != 0) {
            //余2个byte的情况
            if (s.charAt(sLen - 1) == '=') {
                missingBytesInLastGroup++;
                //如果有余数发生，则完整3个byte组数少一个。
                numFullGroups--;
            }
            //余1个byte的情况
            if (s.charAt(sLen - 2) == '=')
                missingBytesInLastGroup++;
        }

        //总字节长度

        byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];
        try {
            int inCursor = 0, outCursor = 0;
            for (int i = 0; i < numFullGroups; i++) {
                int ch0 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch1 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch2 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch3 = base64toInt(s.charAt(inCursor++), base64ToInt);
                result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
                result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
                result[outCursor++] = (byte) ((ch2 << 6) | ch3);
            }
            if (missingBytesInLastGroup != 0) {
                int ch0 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch1 = base64toInt(s.charAt(inCursor++), base64ToInt);
                //不管余1还是余2个byte，肯定要解码一个byte。
                result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
                //如果余2个，即差一个才构成3byte，那么还要解码第二个byte。
                if (missingBytesInLastGroup == 1) {
                    int ch2 = base64toInt(s.charAt(inCursor++), base64ToInt);
                    result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
                }
            }
        } catch (Exception e) {
            throw e;
        }
        return result;
    }

    private static int base64toInt(char c, byte[] alphaToInt) throws Exception {
        int result = alphaToInt[c];
        if (result < 0)
            throw new Exception("illegal index!");//非法索引值
        return result;
    }

    static final byte base64ToInt[] = {-1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1/*原先是62*/, -1, -1, 62/*原先是-1*/, -1/*原先是63*/, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1,
            -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
            13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1,
            63/*原先是-1*/, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};

    /**
     * @param str原始中文字符串
     * @param charset进行二进制字符串转化的字符编码
     * @return 二进制字符串
     */
    public static String encodeBuffer(String str, String charset) {
        if (str == null) {
            str = StringUtils.EMPTY;
        }
        try {
            return Base64Utils.byteArrayToBase64(str.getBytes(charset));
        } catch (UnsupportedEncodingException e) {
            return new String();
        }
    }

    /**
     * 此方法为还原中文字符串转化后的二进制字符串
     *
     * @param str     二进制字符串
     * @param charset 字符编码
     * @return 正常中文字符串
     */
    public static String decodeBuffer(String str, String charset) {
        if (str == null) {
            return str = StringUtils.EMPTY;
        }
        try {
            byte[] byteStr;
            try {
                byteStr = Base64Utils.base64ToByteArray(str.trim());
            } catch (Exception e) {
                return new String();
            }
            return new String(byteStr, charset);
        } catch (UnsupportedEncodingException e) {
            return new String();
        }
    }
}
